As was described in U.S. Pat. No. 5,562,276, issued on Oct. 8, 1996 to the inventor of the instant application and entitled “LOCATOR AND HOLD DOWN SYSTEM FOR A MACHINE” and which is incorporated by reference herein, a vacuum hold down system for a working table facilitated the location and positioning of structures with respect to a work piece which is to be milled, sanded, ground, etc. with a router-type spindle which travels around a work piece, was illustrated. That invention aided the precision of location and stability of any device on the working table.
Further, as was described in U.S. Pat. No. 6,186,567, issued on Feb. 13, 2001 to the inventor of the instant application and entitled “AUTOMATIC CLAMPING AND PLACEMENT HOLDER” and which is incorporated by reference herein, the use of an angled locator block associated with the motor unit which is normally used to drive a router and translated over the table was illustrated to assist manual placement of a locator device which was used to assist the attendant in locating the work piece, as well as a specialized structure for automatic carriage and positioning of such locator devices on the work table. The locator device simply caused the lifting of a lateral stop structure against which the work piece was located before the work piece was locked down. Prior to processing, the lateral stop structure would be retracted using a pressure control line. The lateral stop structure performed no vertical movement of a work piece.
Computer numerical controlled milling machines are used to process sheet and slab type materials of various material composition, shape, and dimensions. Prior to the actual processing of the materials it is necessary to properly and accurately locate the material to be processed within the limits of the working envelope of the machine with respect to the table surface of the machine and the location of the spindle of the machine relative to the intended movements of the spindle of the machine during its operation process. The hold down force necessary to support a work piece against the force from a rotating spindle is significant. Proper hold down force is necessary to maintain the proper location of the part during the machining process so as to insure accurate dimensional stability of the part, prevent vibration during processing, and insure the desired resultant dimensions of the part after processing are accurate. Typically, work holding supports using vacuum attached to both the underside surface of a sheet type material and to the machine table surface are used to forcibly secure the material for processing. Mechanical clamps may be used, however, mechanical clamps which attach to the edge of sheet materials prevent the processing of the edge immediately adjacent to the clamped portion, whereas vacuum driven supports attached to the underside of the material to be processed offer no obstruction to the machining process and allow for complete uninterrupted peripheral and surface processing. A typical flat working table of a machine must provide an absolutely stable platform to support the material to be worked be it a small table or a very large one. The location of the work piece laterally is important, and the vertical location of the work piece is also important.
Three Axis Machine Problem
As to the problems in working a material on a table with a three axis machine, it is important to recognize that the three axis motor driven spindle used on the work table can be precisely controlled in terms of its lateral position on the table (x and y positions) and height over the table (z position) by the computer numerical controller of the milling machine. Because the cutting head on the spindle on a three axis machine cannot tilt, an attempt to cut or grind a smooth angled surface not parallel to the machine work table surface or perpendicular to the spindle axis is not practically possible without the ability to tilt the work piece.
A practical solution to this problem has been to find some way of stably tilting the work piece, while providing a significant holding force to resist the ability of the spindle to move it. A solution used by conventional three axis machines involves the use of a thick, heavy metal plate which typically has to be moved onto the table with a fork lift or overhead lift. The heavy plate is then tiltably supported on the surface of the working table using jacks or pre-formed inserts either of which has to have the capacity to support the substantial weight of the plate, the conventional perpendicular hold down supports to be supported by the plate, as well as the work piece. In some instances a specialized heavy plate is used with a pivot at or near the center, or at one end, such as an axle or hinge, and having specialized jacking screws at one end to produce the angle of tilt.
The “heavy plate system” is typically fabricated at considerable cost. Further, each time a run of work pieces requiring a tilt is to be set up on a three axis machine, the setup time and effort is excessive. The work table has to be cleared, the heavy tilt plate has to be lifted and placed onto the table, then accurately located with respect to the spindle and stabilized with respect to the table at the proper angle. The setup has to be such that the tilted surface provided is absolutely stable. Only then can the remainder of the setup be effected using conventional hold downs located on top of the surface of the plate. The requirement of using a tilt plate and the extra effort for setup is extremely burdensome in terms of cost for the heavy plate, and the time required for setup.
Five Axis Machine Problem
A five axis machine is typically used to work the edge or field of a work piece having a complex shape. The five axis machine is typically used to process complex shaped materials with compound surfaces. Edge work on complex shapes may consist of processing the material perpendicular to the surface at the edge of or in the field of the material but may also involve processing the edge or the internal area of the material at a constant or changing angle to the surface of the material. Conventional hold downs will not work as conventional hold downs require a significant number of completely flat expanses on the bottom side of a work piece parallel to the work table so that a sufficient area of hold down vacuum can be applied, and this is almost never possible with a complex shape. A practical solution has been the construction of a custom made fixture which includes a series of distributed supports of the exact height and lateral distribution to enable a conforming fit and conforming support for the complex shaped object, sometimes referred to as a “bed of nails” type fixture, i.e., “nails” for supports of differing heights that conform to the underside of the irregular shape to be held in position for processing. This type of fixture will typically have its own specific method of hold down which will in turn be highly adapted to the specific shape and openings available on the complex shape. The costs of individual and specific custom made fixtures for each unique shape to be processed is prohibitive. The present invention allows for flexible adaptation of the work holding device to various and different complex shapes.
What is needed is a system which permits a conventional three axis machine to be used to work an angled surface into a material, but without having to use a heavy plate for setup. What is also needed is a system which permits a conventional five axis machine to be used with a complex shaped object to be worked without the need for design and construction of unique custom fixturing. The needed system should be cost effective and not require special, custom made fixtures tailored to a specific application but rather a system that allows flexible adaptation to many varied and different shapes using the same positionable, adjustable hold down devices.